1. Field of the Invention
The invention relates to a micro inertial sensor, and more particularly to a thermal bubble type micro inertial sensor serving as an inclinometer and an accelerometer for sensing variations of position, tilt, and acceleration.
2. Description of the Related Art
Conventional mechanical type inertial sensors, such as an accelerometer and a gyroscope, are indispensable devices for navigation control. However, since the conventional inertial sensor is bulky and expensive in price, it is limited in various applications. Micro inertial sensors based on MEMS (Micro-Electro-Mechanical-System) technology are recently studied and developed well for realistic product. Using the MEMS technology to manufacture a micro inertial sensor, particularly a micro-accelerometer, may make the property of the sensor satisfying the commercial demands. For example, the sensitivity of the micro-accelerometer is higher, even to reach the detectable order of μg. The size of micro-accelerometer also can be miniaturized and the fabrication cost is cheap for mass production. So, it is suitable for applications of consumer electronics such as a vehicle, a joystick, a 3-D mouse, and the like. The associated reference has been disclosed in, for example, “Micromachined Inertial Sensors” to Yazdi et al., as attached to the specification.
In the prior arts, disclosed micro-accelerometers are mostly solid state sensors typically having a movable proof mass with at least one elastic beam for supporting the proof mass. There are various methods for fabricating the micro-accelerometers, which are mainly developed by way of silicon micromachining technology including polysilicon surface micromachining, as disclosed in U.S. Pat. Nos. 6,223,598B1; 5,487,305; 5,417,111; 5,565,625; 5,817,942 and 5,665,915; and SOI (Silicon on Insulator) surface micromachining, as disclosed in U.S. Pat. Nos. 6,294,400B1; 5,495,761; 5,747,353 and 5,447,067. However, the maximum drawback of such structures is that the fabrication yield rate is low and the elastically supported proof mass may be damaged by sticking effects or external shock forces.
Consequently, a gas convective accelerometer is developed, in which the natural principle of gas convection is utilized to replace the moveable proof mass in order to overcome the above-mentioned drawbacks, as disclosed in U.S. Pat. Nos. 2,445,394; 2,554,512; 3,241,374; and 5,581,034. The methods for forming the gas convective accelerometer by way of micromachining are disclosed in U.S. Pat. Nos. 5,719,333; 6,171,880; and 6,182,509. However, since the heat transfer speed of the gas is slow, the response speed of this gas convective accelerometer is quite slow (about 30 Hz), which limits its application. Moreover, since the accelerometer has to be packaged in a sealed chamber to control the environment pressure, the cost is greatly increased.
In view of this, the invention discloses a novel sensing mechanism to overcome the above-mentioned problems, wherein a thermal bubble type micro inertial sensor serves as an inclinometer or an accelerometer to achieve the advantages of quick response speed without a proof mass.